US 3518773 A
Description (OCR text may contain errors)
July 7, 1970 E. S. JOHANSON 125 uon-connsuslms couosusmmn AND 21 summon 20 1a 1 r I -17 GRINDINGAND 1 name srem SLURRY0lL36/ HEATER 19 1 I I 30 REACTOR38 28 Z VENTGASES40 3 v HEDIUMSIZEJ 34 7 SOLID PRODUCTS 44 C0AL10* swam TANK 32 IEATED/ V was ;AS12
INVENTORI EDWIN S. JOHANSON AGENT United States Patent 3,518,773 SOLIDS DRYING PROCESS Edwin S. Johanson, Princeton, N.J., assignor to Hydrocarbon Research, Inc., New York, N.Y., a corporation of New Jersey Filed Feb. 29, 1968, Ser. No. 709,468 Int. Cl. F27b 5/00 U.S. Cl. 34-26 9 Claims ABSTRACT OF THE DISCLOSURE A process for removing moisture from a fine particulate solid material by contacting a drying gas with the particulate material. The use of a readily condensible gas for the drying gas is disclosed with subsequent condensing of the gas after the contacting step, whereby the fines contained in said gas may be recovered from the condensate.
BACKGROUND OF THE INVENTION This invention pertains to the field of moisture removal from particulate solids. More specifically, it relates to the drying of carbonaceous material such as, coal, lignite or peat prior to its introduction into a coal conversion process for the purposes of making hydrocarbon products from the coal.
Typically, the coal conversion processes which are known to the art require the pulverizing and drying of the coal, followed usually, by a slurrying of the pulverized coal into a hydrocarbon liquid and then subjecting said slurry to a hydrocracking and/or hydrogenation. Both catalytic and noncatalytic processes are known in the art.
Examples of such processes are described in the Johanson U.S. Pat. Re. 25,770 and the Schuman et a1. patent,
U.S. Pat. No. 3,321,393. In this type of process, the dried, pulverized coal is slurried with an oil from the process and is then passed upwardly with hydrogen through a catalytic bed at such velocity whereby the bed exists in an expanded or ebullated state. A major requirement of such processes is that the coal be substantially free of moisture, since such moisture results in excessive foaming in the slurry preparation step and reduction of the hydrogen partial pressure in the reaction zone.
The usual methods for drying the coal, incorporate the use of a drying gas which is contacted with the particulate coal either during or after the pulverizing step. A major problem in such a drying step is the excessive retention of fines in the drying gas after the contacting process. The fines present a problem for two reasons: First, they represent a substantial loss in feed material and can prove to be rather expensive from a yield point of view; second, there has been increasing attention drawn to the problem of air pollution in this country today, and the venting of a carbonaceous fines-containing gas to the atmosphere is detrimental to such a situation. Many jurisdictions now have statutory prohibition against introducing such contaminated gases to the atmosphere.
In the past, the drying processes have incorporated filter bags and separation devices of that nature to remove the,
fines from the drying gas, however, such devices have proven to be quite expensive and inefiicient, especially with fines in the 1-5 micron size range. The use of cyclones and devices operating on the centrifugal force principle has been attempted, however, it has been found that the fines particles are too small to be effectively separated by such devices.
SUMMARY OF THE INVENTION I have discovered a method by which fines may be effectively removed from gases that have been contacted with particulate solids for drying purposes and, which also renders the fines amenable to subsequent downstream processing. My invention is particularly useful with respect to known methods of separation of fines, since it allows one to efficiently utilize a centrifugal force device to separate the fines from the drying gas.
I have found that by using an inert, readily-condensable gas as the drying gas, I can accomplish the desired moisture removal from the particulate material and subsequent to such moisture removal, subject the gas to condensation conditions whereby the fines are retained in the condensate and are readily removable therefrom.
The separation methods used may be any of those known in the art, e.g., simple settling devices, evaporators, etc. More particularly, however, my invention is specifically useful with a centrifugal force type device, such as a cyclone. In such a case, the condensation conditions may easily be adjusted such that nuclear condensation is effected, whereby the readily condensable gas liquefies in a mist or foglike manner. The fines in the gas act as nucleating sites for the mist particles and these nucleated mist particles then have sufficient weight to be centrifuged from the noncondensed gas.
It is a further object of my invention to use readily condensable materials, such as hydrocarbons which are compatible with the coal conversion process, whereby the fines-containing condensate may be directly introduced to the conversion reaction zone without additional intermediate separation steps.
Thus, by use of my invention, one may recover a substantial amount of feed material which would normally be lost from the process and, at the same time, avoid producing an air-contaminating waste.
DESCRIPTION OF THE DRAWING The drawing is a schematic flow diagram of a coal grinding and drying process incorporated in a coal conversion process.
DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, coal at 10 having a size in the range of about 1%" diameter, is introduced along with a drying gas at 12 to a grinding and drying zone 14. The drying gas consists of a readily-condensible inert gas which has been heated in heater 19 to a temperature sufficient to remove moisture from the pulverized coal. Temperatures within the range of about 200 F. to about 600 F. are normal for such an operation. By inert, it is meant that the gas does not react in any way with the carbonaceous material except for supplying the heat and carrying medium for removing the moisture therefrom. The designation readily-condensible is meant to include all those gases which have boiling points which would allow them to be liquefied within the reasonable temperature parameters of a drying process of this nature. It would be expected, for instance, that materials which had boiling points within the range of above F. preferably at least ambient temperatures to perhaps, about 300 F. would be suitable. One would not, for example, think of oxygen, nitrogen or carbon dioxide as being suitable for this process, as they are not considered to be readilycondensable. Gases, on the other hand, such as superheated steam and hydrocarbon materials, both aliphatic and aromatic, boiling within the range from about 100 F. to about 300 F, can be used for this process.
The grinding and drying step may be carried out simultaneously or the coal feed may be ground separately and then dried. There are a number of contacting processes known to the art which can be utilized in step 14, e.g., a fluidized bed.
The moisture and fines-containing gas is removed overhead through line 16 to enter a cyclonic step 17 that separates from the vapors, the readily removed, medium sized solids which pass directly through line 30 to the slurry preparation system 32. A portion of the vapors from step 17, equal in quantity to the drying gas, passes through line 18 to be reheated in heater 19. The balance of the vapors, which contain the moisture removed from the coal, are removed through line 21 to condensation and separation step 20.
A particular advantage of my invention is that the amount of vapor removed to the condensation step from the cyclone 17 is only that required to carry the total moisture removed from the coal. The major portion of the drying gas is reheated and recirculated. Thus, there is no drying gas exited from the process. In practice, of course, small make up portions would be required from time to time.
The condensation of the readily-condensable gas may be effected simply by reducing the temperature of the vapor in line 21 to a sufiicient level to liquefy the gas. One method of accomplishing this temperature reduction is by shunting a portion of a cooled gas such as the noncondensable in line 22 through line 25 into line 21. This type of cooling is particularly effective in that it will favor mist formation through the vapors rather than condensation on the conduit and separation zone surfaces. Other methods of cooling would include water or hydrocarbon liquid injection.
The separation step may be effected by gravity means or, if desired, can incorporate a centrifugal force type device, such as cyclones, or centrifuges in which case, a net water efiluent, free from fines, is removed in line 23. The condensate and the fines are removed through line 24. If the drying gas is a linear or cyclic aliphatic hydrocarbon or an aromatic hydrocarbon, i.e., compatible with those materials in the reaction zone, the condensate and fines may be introduced to the slurry tank 32 through line 28. In slurry tank 32, a slurry of the dried pulverized coal from line and slurry oil in line 36, is prepared. The mixture then proceeds to the reaction zone 38 wherein the coal is converted to products which are removed in line 44; slurry oil which is removed in line 36 and recycled to the slurry tank; and vent gases in line 40. As mentioned above, the vent gases may be used as the drying gas in the grinding and drying step.
If it is desired to introduce the condensate into the reaction zone, it is necessary that the water which it contains be removed prior to such introduction. The removal of the water may be effected by normal fractionation methods. It is preferable, of course, that the condensation step be operated at a condition whereby the water will be removed through line 22 with the noncondensable gases or as liquid free of fines through line 23. The removal of the water as a vapor would essentially limit the minimum temperature of the step to about 212 F. If such temperature requirements are not feasible, however, there are numerous methods known to the art whereby water may be removed from the nonaqueous liquid condensate.
When steam is the drying gas, it is heated to about 500 F. and approximately ten pounds of steam per pound of water to be removed from the solids is used. As described above, the steam is contacted with the coal at a temperature of about 240 F. The gas issuing from the drying zone is now 11 parts steam vapor and after cyclone step 17, it is split into ten parts which are recirculated through the heater 19 and one part which is introduced to condensation and separation step 20 wherein some or all of the steam is condensed by indirect heat exchange or by direct introduction of a quench medium, e.g., condensed water or gas as in line 25.
As previously mentioned, an organic material such as a linear or aliphatic hydrocarbon or aromatic hydrocarbon may be used as the drying gas. An example of this mode of operation is the use of a gas composed of 82 percent by weight of a hydrocarbon having a boiling point of about 275 F. and 18 percent by weight Water vapor.
Thus, for the removal of one pound of water, the drying gas contains 7.6 pounds of hydrocarbon and 1.6 pounds of water vapor. The gas exiting from the drying step, i.e., cyclone 17, contains 7.6 pounds of hydrocarbon and 2.6 pounds of water vapor. To shunt the one pound of removed water to the condensation step 20, a total of 3.9 pounds of gas is removed in line 21, said gas containing 2.9 pounds of hydrocarbon. The remaining 4.7 pounds of hydrocarbon and 1.6 pounds of water would be recirculated to heater 19. The gas in line 21 is cooled to about 200 F. using the heretofore described methods. The water contained in this stream will not condense due to its reduced partial pressure, whereas about /3 or about 0.9 pound of the hydrocarbon condenses on the nucleus of the coal fines. Thus, with a carryover of fine solids of about ten weight percent of the water vaporized, the concentration of solids in the condensate is about eleven weight percent. The condensate and fines are then separated and removed through line 24 and introduced to the slurry tank through line 28.
The uncondensed water vapor with some gaseous hydrocarbon at 200 F. in line 22 is further cooled and condensed. It is a relatively simple operation to separate the immiscible hydrocarbons and water. The separated hydrocarbons are then either reused for makeup in the drying gas or added to the slurry.
Obviously, many modifications and variations of the invention as hereinabove set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.
1. In a process for removing moisture from a particulate carbonaceous material of the type wherein a hot, inert drying gas is contacted with the particulate material and wherein after the contacting step, the gas contains moisture and fines consisting essentially of the carbonaceous material, the improvement which comprises using a readily-condensable gas selected from the group consisting of superheated steam and linear and cyclic aliphatic and aromatic hydrocarbons having a boiling range from about to about 300 F. as the inert gas and condensing said gas after the contacting step whereby the fines may be recovered with the condensate.
2. The process as claimed in claim 1 wherein the carbonaceous material is coal which is being dried for subsequent conversion to liquid and gaseous products in a hydrogenation zone.
3. The process as claimed in claim 2 wherein the drying gas contains an organic material selected from the group consisting of aliphatic and aromatic hydrocarbons boiling within the range from about F. to about 300 F. or combinations thereof.
4. The process as claimed in claim 3 wherein a substantial amount of the organic material contained in the drying gas is condensed after the contacting step without condensing the water vapor contained therein and wherein the fines-containing condensate is introduced to the hydrogenation zone.
5. The process as claimed in claim 4 wherein the drying gas contains a hydrocarbon material having a boiling point of about 275 F. and wherein the drying gas is cooled to a temperature of about 200 F., whereby said hydrocarbon material condenses without condensation of any water vapor contained in the drying gas.
6. The process as claimed in claim 2 wherein the drying gas is superheated steam.
7. The process as claimed in claim 6 which further includes the steps of:
(a) heating the steam to about 500 F. prior to the contacting step and then;
(b) contacting the steam with the solid at a rate of about ten pounds of steam per pound of water to be 5 removed from the solid and at a temperature of about 240 F. and then;
(c) exiting the steam from the contacting step and then;
(d) splitting the steam into a major portion equal to the amount of steam originally entering the contacting step and a minor portion equal to the amount of water removed from the solid and then;
(e) recirculating the major portion to the heating step and;
(f) condensing all or part of the minor portion.
8. The process as claimed in claim 2 wherein the drying gas is condensed by introducing a cooling material selected from the group consisting of water, steam,
whereby the condensate liquefies as mist-like droplets, said droplets being nucleated by the fines contained in the gas.
9. The process as claimed in claim 8 wherein the nucleated droplets are removed from the gas 'by centrifugation.
References Cited UNITED STATES PATENTS 2,843,942 7/1958 Whitsel 3436 XR JOHN J. CAMBY, Primary Examiner US. Cl. X.R.
and liquid and gaseous hydrocarbons to the drying gas 15 3436